A simplified typical air conditioning or refrigeration cycle includes transferring heat into a refrigerant, pumping the refrigerant to a place where heat can be removed from it, and removing the heat from the refrigerant. A refrigerant is a fluid that picks up heat by evaporating at a low temperature and pressure and gives up heat by condensing at a higher temperature and pressure. In a closed system, the refrigerant is then cycled back to the original location where heat is transferred into it. In a mechanical system, a compressor converts the refrigerant from a low temperature and low pressure fluid to a higher temperature and higher pressure fluid. After the compressor converts the refrigerant, a condenser is used to liquefy the fluid (gas) by cooling during the condensing part of the cycle. In operation, hot discharge gas (refrigerant vapor) from the compressor enters the condenser coil at the top, condenses into a liquid as heat is transferred to the outdoors. The refrigerant then passes through a metering device, such as an expansion valve, where it is converted to a low temperature, low pressure fluid before entering an evaporator.
Condensers typically use either water or air to remove heat from the refrigerant. Air-cooled condensers typically pipe the refrigerant through a coil of ample surface across which air is blown by a fan or induced natural draft. Air-cooled condensers can operate in relatively dusty environments where dust settles on the coil. Too much dust on the coil of a condenser severely degrades the performance of the refrigeration or air conditioning unit. Unit operation becomes more expensive due to the higher input power required. In extreme conditions, a dirty condenser may cause a high-pressure safety trip during hot days. Manufacturers recommend that the condenser coil be kept clean, but it is difficult for a user to tell how often a condenser should be inspected, since the frequency of inspection depends on the environment and the frequency of operation of the unit. Having information concerning condenser coil cleanliness on a real time basis would be useful to the user in optimizing a cleaning schedule.